1. Field
Embodiments relate to magneto-photonics and a nanotechnology field, and more particularly, to methods of amplifying magneto-optical effects.
2. Description of the Related Art
Properties and application methods with respect to magneto-photon materials have been researched and developed for many decades (e.g., A. B. Granovskii, E. A. Gan'shina, A. N. Yurasov, Yu. V. Boriskina, S. G. Yerokhin, A. B. Khanikaev, M. Inoue, A. P. Vinogradov, Yu. P. Sukhorukov, Magneto-refractive effect in nanostructures, manganite and magneto-photonic crystals, Radiotekhnika i Elektronika, Vol. 52, No. 9, pp. 1152-1159 (2007)). Magneto-photon materials can be used in making optoelectronic devices, communication systems and a computer technology which are controlled by a magnetic field. Separately, there has also been research conducted on the application of inverted opals based on metals and alloys with respect to magnetoplasmonics, particularly, with respect to the manufacture of plasmon circuits.
The magneto-optical effects created by rotating a polarization plane of a light beam that is transmitted through a transparent medium in a magnetic field (Faraday effect) or reflected from a magnetized medium (Kerr effect) were relevant only in a purely theoretical way for a long time due to small values of rotation angles of the polarization plane. However, in recent decades, important and practical applications have been found. Recently, interest with respect to the magneto-optical effects has increased due to their applications in the fields of physics, optics and electronics.
A feature of the magneto-optical effects is non-reciprocity, i.e. a disturbance of a reversibility principle of a light beam. A change in a reverse direction of the light beam results in the same rotation angle of a polarization plane in the same direction on a “forward” trajectory. Therefore, the magneto-optical effects are accumulated by repeatedly transmitting the light beam that passes through a magnetic material. Multiple reflections of the light beam in a medium are possible because of a dielectric constant of a material which is spatially modulated. The material (that has become recently widely known as a photon crystal) has photon forbidden zones which occur due to repeated Bragg reflection of electromagnetic waves on a periodic disturbance of a dielectric constant and may be used to magnify an interaction efficiency of light with a medium. In this regard, magnetic inverted opals have created interest related to a capability of making optical devices to be controlled by an external magnetic field based on the magneto-optical effects.
The value of the Kerr effect can be defined as an efficiency of interaction between light and a magnetized material. Although light is strongly reflected from a conductor below a frequency of plasma oscillations, the light penetrates with a depth of a skin-layer that is a limit in which interaction with a material occurs. Here, the frequency of the plasma oscillations may be given, in an SGS system, as ωp≈(4πne2/m)½ where n indicates a conduction electron density, e indicates a charge, and m indicates an electronic mass. Also, the depth of the skin-layer may be δ=c/(2πσμω)½ (σ—specific conductivity). Thus, a plasmon-polarized wave that represents interconnected oscillations of electrons and an electromagnetic field may be on a metal surface, as a result of interaction between the light and the free charge carriers. The plasmon-polarized wave that occurs on the metal surface results in amplification of the interaction between the light and the material. The more the plasmon-polarized wave is effectively generated, the more the Kerr effect is strongly displayed.
The plasmon-polarized wave on and under the metal surface is defined by Equations 1 and 2.
                                                        E              z                              (                1                )                                      ⁡                          (                              x                ,                z                            )                                =                                    E              0                        ⁢                          exp              ⁡                              (                                                      -                                          α                      1                                                        ⁢                  z                                )                                      ⁢                          exp              ⁡                              (                                  ⅈ                  ⁢                                                                          ⁢                                      k                    P                                    ⁢                  x                                )                                                    ,                                  ⁢                                            E              z                              (                2                )                                      ⁡                          (                              x                ,                z                            )                                =                                    E              0                        ⁢                          exp              ⁡                              (                                                      α                    2                                    ⁢                  z                                )                                      ⁢                          exp              ⁡                              (                                  ⅈ                  ⁢                                                                          ⁢                                      k                    P                                    ⁢                  x                                )                                                    ,                            (                  Equation          ⁢                                          ⁢          1                )                                                      k            p                    =                                    (                              ω                c                            )                        ⁢                                                                                ɛ                    1                                    ⁢                                      ɛ                    2                                                                                        ɛ                    1                                    +                                      ɛ                    2                                                                                      ,                                  ⁢                              α                          1              ,              2                                =                                    (                              ω                c                            )                        ⁢                                                            -                                                            ɛ                                              1                        ,                        2                                            2                                                                                      ɛ                        1                                            +                                              ɛ                        2                                                                                                        .                                                          (                  Equation          ⁢                                          ⁢          2                )            
Here, kp indicates a wave number of the plasmon-polarized wave, ∈1 indicates a dielectric constant of a medium on metal (∈1>0, in vacuum ∈1=1), and ∈2 indicates a dielectric constant in the metal (∈2<0, |∈2|>∈1). A modulus of the dielectric constant ∈2 of the metal is decreased with growth of a frequency, and the decrease results in deviation of ω(kp) of the plasmon-polarized wave from a linear dependence. However, branches ω(k) for usual light and ω(kp) for the plasmon-polarized wave do not directly cross each other, and thus, it is impossible to achieve an impulse of light k·sin θ=kp that is a requirement to preserve a component in parallel with the metal surface (where θ indicates an incidence angle of a light beam). However, if the metal has a periodic structure with a period G=2 π/d in a k-space (where d indicates a structure period in a direct space) in an X-axis direction, the wave numbers that differ from each other in a value G may be physically equivalent and thus excitation of the plasmon-polarized wave may have a wave number kp that satisfies Equation 3 below.k sin θ=kp±G  (Equation 3)
In a more general case, k·sin θ=kP+mG, in Equation 3, where m indicates an arbitrary integer. In particular, the requirement of Equation 3 may be achieved by a wave length given via Equation 4.
                              λ          Wood                =                  ⅆ                      (                                                                                                      ɛ                      1                                        ⁢                                          ɛ                      2                                                                                                  ɛ                      1                                        +                                          ɛ                      2                                                                                  +                              sin                ⁢                                                                  ⁢                θ                                      )                                              (                  Equation          ⁢                                          ⁢          4                )            
In this case, effective generation of the plasmon-polarized wave on the metal surface leads to a ‘Wood feature’ that is a sharp decrease in intensity of a reflected light which causes a minimum value in a reflection spectrum.
Thus, there is a theoretical basis for the concept that the magneto-optical Kerr effect may be amplified by making a periodically-structured surface of a magnetic material, in particular, a magnetic inverted opal.
Recently, several examples with respect to the use of photon-crystal mediums that amplify interaction between light and a medium have been developed. However, these examples are restricted by the use of photon crystals in refracting optics, whereas the technology of reflecting optics based on photon crystals has not been practically developed. The methods of forming photon-crystal reflecting surfaces, which are applied at present, have insufficient flexibility, and thus do not provide an exact control of surface morphology or a desired application with respect to lithographic approaches which predetermine a complex application of photon-crystal structures as optical components based on reflection that can be controlled by an external field.
U.S. Pat. No. 7,965,436 discloses a device, performing rotation of a polarization plane of light and method of its manufacturing. The disclosed device is characterized by the following features: the device consists of a nonmagnetic dielectric wave guide and a magnetic shell around the nonmagnetic dielectric wave guide; a nonmagnetic wave guide is the siliceous photon crystal obtained by perforation via a lithographic technology; a thickness of a photon crystal lies within a range from 50 to 400 nanometers, and perforation has a periodic structure along an axis of a wave guide and has a period from 200 to 800 nanometers, and each hole has a diameter from 50 to 100 nanometers; and a device having a length of two micrometers performs circular rotation of a polarization plane of the wave transmitted on the wave guide by 45 degrees.
The disclosed solution has been chosen as a prototype to be used in a method of amplifying a magneto-optical Kerr effect by using the photon-crystal structures. However, the disclosed solution cannot be applied to amplify interactions between light and a medium at reflection.